I finally received a replacement flyback transformer for this beauty today. Took a while for Dönberg Electronics to get it in stock but I'm thankful that were actually able to source a flyback for a vintage CRT. Obviously I haven't had time to install the new fly yet but I can certainly attest to Dönberg's service. They're really helpful and are serious about what they do. Also, they wrap a pretty mean parcel!
Package from Dönberg
HR 6504 flyback
Grundig 29221-029.05 replacement
I really hope it's as simple as just soldering this into the chassis and having life breathed back into the telly. Hopefully nothing else was taken out when the original flyback went up in smoke... I guess we'll see when I find some time for this epic operation!